| Subash Abhinov Kasiviswanathan | ceed73a | 2017-08-29 22:44:18 -0600 | [diff] [blame] | 1 | 1. Introduction |
| 2 | |
| 3 | rmnet driver is used for supporting the Multiplexing and aggregation |
| 4 | Protocol (MAP). This protocol is used by all recent chipsets using Qualcomm |
| 5 | Technologies, Inc. modems. |
| 6 | |
| 7 | This driver can be used to register onto any physical network device in |
| 8 | IP mode. Physical transports include USB, HSIC, PCIe and IP accelerator. |
| 9 | |
| 10 | Multiplexing allows for creation of logical netdevices (rmnet devices) to |
| 11 | handle multiple private data networks (PDN) like a default internet, tethering, |
| 12 | multimedia messaging service (MMS) or IP media subsystem (IMS). Hardware sends |
| 13 | packets with MAP headers to rmnet. Based on the multiplexer id, rmnet |
| 14 | routes to the appropriate PDN after removing the MAP header. |
| 15 | |
| 16 | Aggregation is required to achieve high data rates. This involves hardware |
| 17 | sending aggregated bunch of MAP frames. rmnet driver will de-aggregate |
| 18 | these MAP frames and send them to appropriate PDN's. |
| 19 | |
| 20 | 2. Packet format |
| 21 | |
| 22 | a. MAP packet (data / control) |
| 23 | |
| 24 | MAP header has the same endianness of the IP packet. |
| 25 | |
| 26 | Packet format - |
| 27 | |
| 28 | Bit 0 1 2-7 8 - 15 16 - 31 |
| 29 | Function Command / Data Reserved Pad Multiplexer ID Payload length |
| 30 | Bit 32 - x |
| 31 | Function Raw Bytes |
| 32 | |
| 33 | Command (1)/ Data (0) bit value is to indicate if the packet is a MAP command |
| 34 | or data packet. Control packet is used for transport level flow control. Data |
| 35 | packets are standard IP packets. |
| 36 | |
| 37 | Reserved bits are usually zeroed out and to be ignored by receiver. |
| 38 | |
| 39 | Padding is number of bytes to be added for 4 byte alignment if required by |
| 40 | hardware. |
| 41 | |
| 42 | Multiplexer ID is to indicate the PDN on which data has to be sent. |
| 43 | |
| 44 | Payload length includes the padding length but does not include MAP header |
| 45 | length. |
| 46 | |
| 47 | b. MAP packet (command specific) |
| 48 | |
| 49 | Bit 0 1 2-7 8 - 15 16 - 31 |
| 50 | Function Command Reserved Pad Multiplexer ID Payload length |
| 51 | Bit 32 - 39 40 - 45 46 - 47 48 - 63 |
| 52 | Function Command name Reserved Command Type Reserved |
| 53 | Bit 64 - 95 |
| 54 | Function Transaction ID |
| 55 | Bit 96 - 127 |
| 56 | Function Command data |
| 57 | |
| 58 | Command 1 indicates disabling flow while 2 is enabling flow |
| 59 | |
| 60 | Command types - |
| 61 | 0 for MAP command request |
| 62 | 1 is to acknowledge the receipt of a command |
| 63 | 2 is for unsupported commands |
| 64 | 3 is for error during processing of commands |
| 65 | |
| 66 | c. Aggregation |
| 67 | |
| 68 | Aggregation is multiple MAP packets (can be data or command) delivered to |
| 69 | rmnet in a single linear skb. rmnet will process the individual |
| 70 | packets and either ACK the MAP command or deliver the IP packet to the |
| 71 | network stack as needed |
| 72 | |
| 73 | MAP header|IP Packet|Optional padding|MAP header|IP Packet|Optional padding.... |
| 74 | MAP header|IP Packet|Optional padding|MAP header|Command Packet|Optional pad... |
| 75 | |
| 76 | 3. Userspace configuration |
| 77 | |
| 78 | rmnet userspace configuration is done through netlink library librmnetctl |
| 79 | and command line utility rmnetcli. Utility is hosted in codeaurora forum git. |
| 80 | The driver uses rtnl_link_ops for communication. |
| 81 | |
| 82 | https://source.codeaurora.org/quic/la/platform/vendor/qcom-opensource/dataservices/tree/rmnetctl |